A question about 36V vs 48V solenoid

[rlw]

Originally Posted by rlw

I got the idea from Ohm's Law....

Duhhhhhh!

I *did* have my head firmly planted in my nether regions!

I was inverting the current calculation in my firmly planted head - instead of I=E/R, I was thinking I=R/E.

Duhhhh!

Sorry for stupid post. My bad.

RLW

[cgtech]

To all who believe that increasing voltage will reduce amps, please see below.

[JohnnieB]

Some confusion occurs due to the fact motors convert Watts into Torque and more confusion occurs due to the fact that the dynamic impedance (resistance) of a motor increases as the applied voltage increases as well as when the RPM increases.

At the same RPM and under the same load (mechanical drag) a motor will draw fewer amps at a higher voltage than it does at a lower voltage since the number of Watts used will be the same and Watts = Amps x Volts.

If a 36V golf cart's motor draws 80A cruising on level ground at 20 MPH, 2,880W are being converted into motion and if the pack voltage is increased to 48V, only 60A will be needed to propel the same cart over the same terrain with the same weight on board.

What happens is that the dynamic impedance of the motor changes due to the change in voltage, so Ohm's Law holds true.

On the other hand, in a resistor cart, fixed resistors are place in series with the motor to limit the current flow through the motor and increasing the voltage on a fixed resistor does increase current flow, and the heat generated in the resistor coils increases exponentially with current flow, (W = I^2 x R) so they soon burn out from the increased heating.


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If you can figure out how to add an additional battery or two only when the throttle was in the direct battery connection position and not going through the resistor coils, it would work.

[cgtech]

While all this is true, almost nobody who desires to upgrade their system from 36v to 48v wants to only use 2/3 to 3/4 of their throttle (load) or rpms (speed) after ther conversion is complete. They wanted increased performance, not the same performance with better efficency. With this taken into consideration, the watt loads (and overall amp-hour loads) will increase with a typical 48v conversion (resistor coils or solid-state).

[JohnnieB]

Originally Posted by cgtech

1. While all this is true, almost nobody who desires to upgrade their system from 36v to 48v wants to only use 2/3 to 3/4 of their throttle (load) or rpms (speed) after ther conversion is complete. They wanted increased performance, not the same performance with better efficency.
2. With this taken into consideration, the watt loads (and overall amp-hour loads) will increase with a typical 48v conversion (resistor coils or solid-state).

1. I didn't claim it was practical, just that it could be done.
Basically a 36V resistor cart for the first 3 speeds with the speed of a 48V cart when the pedal is on the floor.

IIRC, there are some plans floating around here someplace (Posted by Roady?) using solenoids or switches to connect additional batteries to reach a higher top speed in controller carts without upping the controller and solenoid voltage. (Or it might have bypassed the controller entirely, I don't remember.) Anyway, I believe the same concept could work with a resistor cart, if you could figure out a way that the boost solenoid(s) could only be activated when the throttle's wiper was landed on the last contact.

Of course, if I was doing a resistor cart, I'd probably drop in a 6 x 8V battery pack and a 48V controller & solenoid with a 0-5k throttle input and add fixed resistors to the existing wiper and stud throttle system and send that to the controller as the throttle signal, to give me a five speed cart. (See attached)


2. That is true, but it's due to human nature rather than any of the laws of physics.
For some reason, one's right foot gets heavier when one ups the pack voltage.

My stock PDS motor got hotter running on 42V than it did on 36V, using the same DCX400 controller.
I suspect that was because I was hitting it with 14,400W off the line at 36V and 16,800W at 42V, or at least had the potential of doing so.

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I can disconnect one battery and run at 36V, and I still have a 36V charger, so I could drive flat out over the same terrain at 36V and 42V while saving the data log files and compare them, but that adds another project to my bucket list, so I probably won't.

[HiTechRedNeck]

JohhnieB -- "I can disconnect one battery and run at 36V, and I still have a 36V charger, so I could drive flat out over the same terrain at 36V and 42V while saving the data log files and compare them, but that adds another project to my bucket list, so I probably won't. "


Waiting for you to test drive and review an RXV first...
Then you can waste time on those other projects.

[rlw]

Hey all,

Sorry (again!) for the thread that was a result of my upside-down thinking, but at least it got an interesting and lively discussion going...

I learn something new every time I start pokin' around on BGW.

Thanks,

RLW